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    GitHub
    <span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></nav>  <ul class="sidebar-links"><li><a href="/vdoing-demo-repository/pages/c438df/" class="sidebar-link">01_认识 Python</a></li><li><a href="/vdoing-demo-repository/pages/54ff73/" class="sidebar-link">02_第一个 Python 程序</a></li><li><a href="/vdoing-demo-repository/pages/d84b0c/" class="sidebar-link">03_PyCharm 的初始设置(知道)</a></li><li><a href="/vdoing-demo-repository/pages/d99c19/" class="sidebar-link">04_多文件项目的演练</a></li><li><a href="/vdoing-demo-repository/pages/6bdfff/" class="sidebar-link">05_注释</a></li><li><a href="/vdoing-demo-repository/pages/20b1cf/" class="sidebar-link">06_算数运算符</a></li><li><a href="/vdoing-demo-repository/pages/82298a/" class="sidebar-link">07_程序执行原理(科普)</a></li><li><a href="/vdoing-demo-repository/pages/9b2741/" class="sidebar-link">08_变量的基本使用</a></li><li><a href="/vdoing-demo-repository/pages/3e8319/" class="sidebar-link">09_变量的命名</a></li><li><a href="/vdoing-demo-repository/pages/a02b0a/" aria-current="page" class="active sidebar-link">10_判断语句</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header level2"><a href="/vdoing-demo-repository/pages/a02b0a/#目标" class="sidebar-link">目标</a></li><li class="sidebar-sub-header level2"><a href="/vdoing-demo-repository/pages/a02b0a/#_01-开发中的应用场景" class="sidebar-link">01. 开发中的应用场景</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header level3"><a href="/vdoing-demo-repository/pages/a02b0a/#程序中的判断" class="sidebar-link">程序中的判断</a></li><li class="sidebar-sub-header level3"><a href="/vdoing-demo-repository/pages/a02b0a/#判断的定义" class="sidebar-link">判断的定义</a></li></ul></li><li class="sidebar-sub-header level2"><a href="/vdoing-demo-repository/pages/a02b0a/#_02-if-语句体验" class="sidebar-link">02. if 语句体验</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header level3"><a href="/vdoing-demo-repository/pages/a02b0a/#_2-1-if-判断语句基本语法" class="sidebar-link">2.1 if 判断语句基本语法</a></li><li class="sidebar-sub-header level3"><a href="/vdoing-demo-repository/pages/a02b0a/#_2-2-判断语句演练-判断年龄" class="sidebar-link">2.2 判断语句演练 —— 判断年龄</a></li><li class="sidebar-sub-header level3"><a href="/vdoing-demo-repository/pages/a02b0a/#_2-3-else-处理条件不满足的情况" class="sidebar-link">2.3 else 处理条件不满足的情况</a></li><li class="sidebar-sub-header level3"><a href="/vdoing-demo-repository/pages/a02b0a/#_2-4-判断语句演练-判断年龄改进" class="sidebar-link">2.4 判断语句演练 —— 判断年龄改进</a></li></ul></li><li class="sidebar-sub-header level2"><a href="/vdoing-demo-repository/pages/a02b0a/#_03-逻辑运算" class="sidebar-link">03. 逻辑运算</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header level3"><a href="/vdoing-demo-repository/pages/a02b0a/#_3-1-and" class="sidebar-link">3.1 and</a></li><li class="sidebar-sub-header level3"><a href="/vdoing-demo-repository/pages/a02b0a/#_3-2-or" class="sidebar-link">3.2 or</a></li><li class="sidebar-sub-header level3"><a href="/vdoing-demo-repository/pages/a02b0a/#_3-3-not" class="sidebar-link">3.3 not</a></li></ul></li><li class="sidebar-sub-header level2"><a href="/vdoing-demo-repository/pages/a02b0a/#_04-if-语句进阶" class="sidebar-link">04. if 语句进阶</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header level3"><a href="/vdoing-demo-repository/pages/a02b0a/#_4-1-elif" class="sidebar-link">4.1 elif</a></li><li class="sidebar-sub-header level3"><a href="/vdoing-demo-repository/pages/a02b0a/#_4-2-if-的嵌套" class="sidebar-link">4.2 if 的嵌套</a></li></ul></li><li class="sidebar-sub-header level2"><a href="/vdoing-demo-repository/pages/a02b0a/#_05-综合应用-石头剪刀布" class="sidebar-link">05. 综合应用 —— 石头剪刀布</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header level3"><a href="/vdoing-demo-repository/pages/a02b0a/#_5-1-基础代码实现" class="sidebar-link">5.1 基础代码实现</a></li><li class="sidebar-sub-header level3"><a href="/vdoing-demo-repository/pages/a02b0a/#_5-2-随机数的处理" class="sidebar-link">5.2 随机数的处理</a></li></ul></li></ul></li><li><a href="/vdoing-demo-repository/pages/79d78c/" class="sidebar-link">11_运算符</a></li><li><a href="/vdoing-demo-repository/pages/3ce888/" class="sidebar-link">12_循环</a></li><li><a href="/vdoing-demo-repository/pages/ceea69/" class="sidebar-link">13_函数基础</a></li><li><a href="/vdoing-demo-repository/pages/e158a8/" class="sidebar-link">14_高级变量类型</a></li><li><a href="/vdoing-demo-repository/pages/ed6fdd/" class="sidebar-link">15_名片管理系统(综合应用)</a></li><li><a href="/vdoing-demo-repository/pages/e98ba6/" class="sidebar-link">16_变量进阶(理解)</a></li><li><a href="/vdoing-demo-repository/pages/f99095/" class="sidebar-link">17_函数进阶</a></li></ul> </aside> <div><main class="page"><div class="theme-vdoing-wrapper "><div class="articleInfo-wrap" data-v-06225672><div class="articleInfo" data-v-06225672><ul class="breadcrumbs" data-v-06225672><li data-v-06225672><a href="/vdoing-demo-repository/" title="首页" class="iconfont icon-home router-link-active" data-v-06225672></a></li> <li data-v-06225672><a href="/vdoing-demo-repository/python/#Python" data-v-06225672>Python</a></li></ul> <div class="info" data-v-06225672><!----> <div title="创建时间" class="date iconfont icon-riqi" data-v-06225672><a href="javascript:;" data-v-06225672>2023-04-02</a></div> <!----></div></div></div> <!----> <div class="content-wrapper"><div class="right-menu-wrapper"><div class="right-menu-margin"><div class="right-menu-title">目录</div> <div class="right-menu-content"></div></div></div> <h1><img src="">10_判断语句<!----></h1> <!----> <div class="theme-vdoing-content content__default"><h1 id="判断-if-语句"><a href="#判断-if-语句" class="header-anchor">#</a> 判断（if）语句</h1> <h2 id="目标"><a href="#目标" class="header-anchor">#</a> 目标</h2> <ul><li>开发中的应用场景</li> <li>if 语句体验</li> <li>if 语句进阶</li> <li>综合应用</li></ul> <h2 id="_01-开发中的应用场景"><a href="#_01-开发中的应用场景" class="header-anchor">#</a> 01. 开发中的应用场景</h2> <p>生活中的判断几乎是无所不在的，我们每天都在做各种各样的选择，如果这样？如果那样？……</p> <p><img src="media/14963192801181/001_%E6%9C%AA%E6%88%90%E5%B9%B4%E4%BA%BA%E7%A6%81%E6%AD%A2%E5%85%A5%E5%86%85.jpg" alt="001_未成年人禁止入内-w400"></p> <p><img src="media/14963192801181/002_%E7%81%AB%E8%BD%A6%E7%AB%99%E5%AE%89%E6%A3%80.png" alt="002_火车站安检-w400"></p> <h3 id="程序中的判断"><a href="#程序中的判断" class="header-anchor">#</a> 程序中的判断</h3> <p><img src="media/14963192801181/003_%E5%88%A4%E6%96%AD%E7%A4%BA%E6%84%8F%E5%9B%BE.png" alt="003_判断示意图-w600"></p> <div class="language-python line-numbers-mode"><pre class="language-python"><code><span class="token keyword">if</span> 今天发工资<span class="token punctuation">:</span>

    先还信用卡的钱

    <span class="token keyword">if</span> 有剩余<span class="token punctuation">:</span>

        又可以happy了，O<span class="token punctuation">(</span>∩_∩<span class="token punctuation">)</span>O哈哈<span class="token operator">~</span>

    <span class="token keyword">else</span><span class="token punctuation">:</span>

        噢，no。。。还的等<span class="token number">30</span>天
<span class="token keyword">else</span><span class="token punctuation">:</span>

    盼着发工资
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br></div></div><h3 id="判断的定义"><a href="#判断的定义" class="header-anchor">#</a> 判断的定义</h3> <ul><li>如果 <strong>条件满足</strong>，才能做某件事情，</li> <li>如果 <strong>条件不满足</strong>，就做另外一件事情，或者什么也不做</li></ul> <blockquote><p>正是因为有了判断，才使得程序世界丰富多彩，充满变化！</p> <p><strong>判断语句</strong> 又被称为 “分支语句”，正是因为有了判断，才让程序有了很多的分支</p></blockquote> <h2 id="_02-if-语句体验"><a href="#_02-if-语句体验" class="header-anchor">#</a> 02. if 语句体验</h2> <h3 id="_2-1-if-判断语句基本语法"><a href="#_2-1-if-判断语句基本语法" class="header-anchor">#</a> 2.1 if 判断语句基本语法</h3> <p>在 <code>Python</code> 中，<strong>if 语句</strong> 就是用来进行判断的，格式如下：</p> <div class="language-python line-numbers-mode"><pre class="language-python"><code><span class="token keyword">if</span> 要判断的条件<span class="token punctuation">:</span>
    条件成立时，要做的事情
    ……
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><blockquote><p>注意：代码的缩进为一个 <code>tab</code> 键，或者 <strong>4</strong> 个空格 —— <strong>建议使用空格</strong></p> <ul><li>在 Python 开发中，Tab 和空格不要混用！</li></ul></blockquote> <p><strong>我们可以把整个 if 语句看成一个完整的代码块</strong></p> <p><img src="media/14963192801181/004_if%E8%AF%AD%E5%8F%A5%E6%98%AF%E4%B8%80%E4%B8%AA%E5%AE%8C%E6%95%B4%E7%9A%84%E4%BB%A3%E7%A0%81%E5%9D%971.png" alt="004_if语句是一个完整的代码块1-w400"></p> <h3 id="_2-2-判断语句演练-判断年龄"><a href="#_2-2-判断语句演练-判断年龄" class="header-anchor">#</a> 2.2 判断语句演练 —— 判断年龄</h3> <p><strong>需求</strong></p> <ol><li>定义一个整数变量记录年龄</li> <li>判断是否满 18 岁 （<strong>&gt;=</strong>）</li> <li>如果满 18 岁，允许进网吧嗨皮</li></ol> <div class="language-python line-numbers-mode"><pre class="language-python"><code><span class="token comment"># 1. 定义年龄变量</span>
age <span class="token operator">=</span> <span class="token number">18</span>

<span class="token comment"># 2. 判断是否满 18 岁</span>
<span class="token comment"># if 语句以及缩进部分的代码是一个完整的代码块</span>
<span class="token keyword">if</span> age <span class="token operator">&gt;=</span> <span class="token number">18</span><span class="token punctuation">:</span>
    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;可以进网吧嗨皮……&quot;</span><span class="token punctuation">)</span>

<span class="token comment"># 3. 思考！- 无论条件是否满足都会执行</span>
<span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;这句代码什么时候执行?&quot;</span><span class="token punctuation">)</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br></div></div><p><strong>注意</strong>：</p> <ul><li><code>if</code> 语句以及缩进部分是一个 <strong>完整的代码块</strong></li></ul> <h3 id="_2-3-else-处理条件不满足的情况"><a href="#_2-3-else-处理条件不满足的情况" class="header-anchor">#</a> 2.3 else 处理条件不满足的情况</h3> <p><strong>思考</strong></p> <p>在使用 <code>if</code> 判断时，只能做到满足条件时要做的事情。那如果需要在 <strong>不满足条件的时候</strong>，做某些事情，该如何做呢？</p> <p><strong>答案</strong></p> <p><code>else</code>，格式如下：</p> <div class="language-python line-numbers-mode"><pre class="language-python"><code><span class="token keyword">if</span> 要判断的条件<span class="token punctuation">:</span>
    条件成立时，要做的事情
    ……
<span class="token keyword">else</span><span class="token punctuation">:</span>
    条件不成立时，要做的事情
    ……
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br></div></div><p><strong>注意</strong>：</p> <ul><li><code>if</code> 和 <code>else</code> 语句以及各自的缩进部分共同是一个 <strong>完整的代码块</strong></li></ul> <h3 id="_2-4-判断语句演练-判断年龄改进"><a href="#_2-4-判断语句演练-判断年龄改进" class="header-anchor">#</a> 2.4 判断语句演练 —— 判断年龄改进</h3> <p><strong>需求</strong></p> <ol><li>输入用户年龄</li> <li>判断是否满 18 岁 （<strong>&gt;=</strong>）</li> <li>如果满 18 岁，允许进网吧嗨皮</li> <li>如果未满 18 岁，提示回家写作业</li></ol> <div class="language-python line-numbers-mode"><pre class="language-python"><code><span class="token comment"># 1. 输入用户年龄</span>
age <span class="token operator">=</span> <span class="token builtin">int</span><span class="token punctuation">(</span><span class="token builtin">input</span><span class="token punctuation">(</span><span class="token string">&quot;今年多大了？&quot;</span><span class="token punctuation">)</span><span class="token punctuation">)</span>

<span class="token comment"># 2. 判断是否满 18 岁</span>
<span class="token comment"># if 语句以及缩进部分的代码是一个完整的语法块</span>
<span class="token keyword">if</span> age <span class="token operator">&gt;=</span> <span class="token number">18</span><span class="token punctuation">:</span>
    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;可以进网吧嗨皮……&quot;</span><span class="token punctuation">)</span>
<span class="token keyword">else</span><span class="token punctuation">:</span>
    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;你还没长大，应该回家写作业！&quot;</span><span class="token punctuation">)</span>

<span class="token comment"># 3. 思考！- 无论条件是否满足都会执行</span>
<span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;这句代码什么时候执行?&quot;</span><span class="token punctuation">)</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br></div></div><p><img src="media/14963192801181/005_ifelse%E8%AF%AD%E5%8F%A5%E6%98%AF%E4%B8%80%E4%B8%AA%E5%AE%8C%E6%95%B4%E7%9A%84%E4%BB%A3%E7%A0%81%E5%9D%971.png" alt="005_ifelse语句是一个完整的代码块1-w400"></p> <h2 id="_03-逻辑运算"><a href="#_03-逻辑运算" class="header-anchor">#</a> 03. 逻辑运算</h2> <ul><li>在程序开发中，通常 <strong>在判断条件时</strong>，会需要同时判断多个条件</li> <li>只有多个条件都满足，才能够执行后续代码，这个时候需要使用到 <strong>逻辑运算符</strong></li> <li><strong>逻辑运算符</strong> 可以把 <strong>多个条件</strong> 按照 <strong>逻辑</strong> 进行 <strong>连接</strong>，变成 <strong>更复杂的条件</strong></li> <li>Python 中的 <strong>逻辑运算符</strong> 包括：<strong>与 and</strong>／<strong>或 or</strong>／<strong>非 not</strong> 三种</li></ul> <h3 id="_3-1-and"><a href="#_3-1-and" class="header-anchor">#</a> 3.1 <code>and</code></h3> <div class="language- line-numbers-mode"><pre class="language-text"><code>条件1 and 条件2
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><ul><li><strong>与</strong>／<strong>并且</strong></li> <li>两个条件同时满足，返回 <code>True</code></li> <li>只要有一个不满足，就返回 <code>False</code></li></ul> <table><thead><tr><th style="text-align:center;">条件 1</th> <th style="text-align:center;">条件 2</th> <th style="text-align:center;">结果</th></tr></thead> <tbody><tr><td style="text-align:center;">成立</td> <td style="text-align:center;">成立</td> <td style="text-align:center;">成立</td></tr> <tr><td style="text-align:center;">成立</td> <td style="text-align:center;">不成立</td> <td style="text-align:center;">不成立</td></tr> <tr><td style="text-align:center;">不成立</td> <td style="text-align:center;">成立</td> <td style="text-align:center;">不成立</td></tr> <tr><td style="text-align:center;">不成立</td> <td style="text-align:center;">不成立</td> <td style="text-align:center;">不成立</td></tr></tbody></table> <h3 id="_3-2-or"><a href="#_3-2-or" class="header-anchor">#</a> 3.2 <code>or</code></h3> <div class="language- line-numbers-mode"><pre class="language-text"><code>条件1 or 条件2
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><ul><li><strong>或</strong>／<strong>或者</strong></li> <li>两个条件只要有一个满足，返回 <code>True</code></li> <li>两个条件都不满足，返回 <code>False</code></li></ul> <table><thead><tr><th style="text-align:center;">条件 1</th> <th style="text-align:center;">条件 2</th> <th style="text-align:center;">结果</th></tr></thead> <tbody><tr><td style="text-align:center;">成立</td> <td style="text-align:center;">成立</td> <td style="text-align:center;">成立</td></tr> <tr><td style="text-align:center;">成立</td> <td style="text-align:center;">不成立</td> <td style="text-align:center;">成立</td></tr> <tr><td style="text-align:center;">不成立</td> <td style="text-align:center;">成立</td> <td style="text-align:center;">成立</td></tr> <tr><td style="text-align:center;">不成立</td> <td style="text-align:center;">不成立</td> <td style="text-align:center;">不成立</td></tr></tbody></table> <h3 id="_3-3-not"><a href="#_3-3-not" class="header-anchor">#</a> 3.3 <code>not</code></h3> <div class="language- line-numbers-mode"><pre class="language-text"><code>not 条件
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><ul><li><strong>非</strong>／<strong>不是</strong></li></ul> <table><thead><tr><th style="text-align:center;">条件</th> <th style="text-align:center;">结果</th></tr></thead> <tbody><tr><td style="text-align:center;">成立</td> <td style="text-align:center;">不成立</td></tr> <tr><td style="text-align:center;">不成立</td> <td style="text-align:center;">成立</td></tr></tbody></table> <h4 id="逻辑运算演练"><a href="#逻辑运算演练" class="header-anchor">#</a> 逻辑运算演练</h4> <ol><li>练习1: 定义一个整数变量 <code>age</code>，编写代码判断年龄是否正确
<ul><li>要求人的年龄在 0-120 之间</li></ul></li> <li>练习2: 定义两个整数变量 <code>python_score</code>、<code>c_score</code>，编写代码判断成绩
<ul><li>要求只要有一门成绩 &gt; 60 分就算合格</li></ul></li> <li>练习3: 定义一个布尔型变量 <code>is_employee</code>，编写代码判断是否是本公司员工
<ul><li>如果不是提示不允许入内</li></ul></li></ol> <p>答案 1：</p> <div class="language-python line-numbers-mode"><pre class="language-python"><code><span class="token comment"># 练习1: 定义一个整数变量 age，编写代码判断年龄是否正确</span>
age <span class="token operator">=</span> <span class="token number">100</span>

<span class="token comment"># 要求人的年龄在 0-120 之间</span>
<span class="token keyword">if</span> age <span class="token operator">&gt;=</span> <span class="token number">0</span> <span class="token keyword">and</span> age <span class="token operator">&lt;=</span> <span class="token number">120</span><span class="token punctuation">:</span>
    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;年龄正确&quot;</span><span class="token punctuation">)</span>
<span class="token keyword">else</span><span class="token punctuation">:</span>
    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;年龄不正确&quot;</span><span class="token punctuation">)</span>

</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br></div></div><p>答案 2：</p> <div class="language-python line-numbers-mode"><pre class="language-python"><code><span class="token comment"># 练习2: 定义两个整数变量 python_score、c_score，编写代码判断成绩</span>
python_score <span class="token operator">=</span> <span class="token number">50</span>
c_score <span class="token operator">=</span> <span class="token number">50</span>

<span class="token comment"># 要求只要有一门成绩 &gt; 60 分就算合格</span>
<span class="token keyword">if</span> python_score <span class="token operator">&gt;</span> <span class="token number">60</span> <span class="token keyword">or</span> c_score <span class="token operator">&gt;</span> <span class="token number">60</span><span class="token punctuation">:</span>
    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;考试通过&quot;</span><span class="token punctuation">)</span>
<span class="token keyword">else</span><span class="token punctuation">:</span>
    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;再接再厉！&quot;</span><span class="token punctuation">)</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br></div></div><p>答案 3：</p> <div class="language-python line-numbers-mode"><pre class="language-python"><code><span class="token comment"># 练习3: 定义一个布尔型变量 `is_employee`，编写代码判断是否是本公司员工</span>
is_employee <span class="token operator">=</span> <span class="token boolean">True</span>

<span class="token comment"># 如果不是提示不允许入内</span>
<span class="token keyword">if</span> <span class="token keyword">not</span> is_employee<span class="token punctuation">:</span>
    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;非公勿内&quot;</span><span class="token punctuation">)</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br></div></div><h2 id="_04-if-语句进阶"><a href="#_04-if-语句进阶" class="header-anchor">#</a> 04. if 语句进阶</h2> <h3 id="_4-1-elif"><a href="#_4-1-elif" class="header-anchor">#</a> 4.1 <code>elif</code></h3> <ul><li>在开发中，使用 <code>if</code> 可以 <strong>判断条件</strong></li> <li>使用 <code>else</code> 可以处理 <strong>条件不成立</strong> 的情况</li> <li>但是，如果希望 <strong>再增加一些条件</strong>，<strong>条件不同，需要执行的代码也不同</strong> 时，就可以使用 <code>elif</code></li> <li>语法格式如下：</li></ul> <div class="language-python line-numbers-mode"><pre class="language-python"><code><span class="token keyword">if</span> 条件<span class="token number">1</span><span class="token punctuation">:</span>
    条件<span class="token number">1</span>满足执行的代码
    ……
<span class="token keyword">elif</span> 条件<span class="token number">2</span><span class="token punctuation">:</span>
    条件<span class="token number">2</span>满足时，执行的代码
    ……
<span class="token keyword">elif</span> 条件<span class="token number">3</span><span class="token punctuation">:</span>
    条件<span class="token number">3</span>满足时，执行的代码
    ……
<span class="token keyword">else</span><span class="token punctuation">:</span>
    以上条件都不满足时，执行的代码
    ……
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br></div></div><ul><li>对比逻辑运算符的代码</li></ul> <div class="language-python line-numbers-mode"><pre class="language-python"><code><span class="token keyword">if</span> 条件<span class="token number">1</span> <span class="token keyword">and</span> 条件<span class="token number">2</span><span class="token punctuation">:</span>
    条件<span class="token number">1</span>满足 并且 条件<span class="token number">2</span>满足 执行的代码
    ……
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p><strong>注意</strong></p> <ol><li><code>elif</code> 和 <code>else</code> 都必须和 <code>if</code> 联合使用，而不能单独使用</li> <li>可以将 <code>if</code>、<code>elif</code> 和 <code>else</code> 以及各自缩进的代码，看成一个 <strong>完整的代码块</strong></li></ol> <h4 id="elif-演练-女友的节日"><a href="#elif-演练-女友的节日" class="header-anchor">#</a> elif 演练 —— 女友的节日</h4> <p><strong>需求</strong></p> <ol><li>定义 <code>holiday_name</code> 字符串变量记录节日名称</li> <li>如果是 <strong>情人节</strong> 应该 <strong>买玫瑰</strong>／<strong>看电影</strong></li> <li>如果是 <strong>平安夜</strong> 应该 <strong>买苹果</strong>／<strong>吃大餐</strong></li> <li>如果是 <strong>生日</strong> 应该 <strong>买蛋糕</strong></li> <li>其他的日子每天都是节日啊……</li></ol> <div class="language- line-numbers-mode"><pre class="language-text"><code>holiday_name = &quot;平安夜&quot;

if holiday_name == &quot;情人节&quot;:
    print(&quot;买玫瑰&quot;)
    print(&quot;看电影&quot;)
elif holiday_name == &quot;平安夜&quot;:
    print(&quot;买苹果&quot;)
    print(&quot;吃大餐&quot;)
elif holiday_name == &quot;生日&quot;:
    print(&quot;买蛋糕&quot;)
else:
    print(&quot;每天都是节日啊……&quot;)

</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br></div></div><h3 id="_4-2-if-的嵌套"><a href="#_4-2-if-的嵌套" class="header-anchor">#</a> 4.2 <code>if</code> 的嵌套</h3> <p><img src="media/14963192801181/002_%E7%81%AB%E8%BD%A6%E7%AB%99%E5%AE%89%E6%A3%80.png" alt="002_火车站安检-w400"></p> <blockquote><p><strong>elif</strong> 的应用场景是：<strong>同时</strong> 判断 <strong>多个条件</strong>，所有的条件是 <strong>平级</strong> 的</p></blockquote> <ul><li>在开发中，使用 <code>if</code> 进行条件判断，如果希望 <strong>在条件成立的执行语句中</strong> 再 <strong>增加条件判断</strong>，就可以使用 <strong>if 的嵌套</strong></li> <li><strong>if 的嵌套</strong> 的应用场景就是：<strong>在之前条件满足的前提下，再增加额外的判断</strong></li> <li><strong>if 的嵌套</strong> 的语法格式，<strong>除了缩进之外</strong> 和之前的没有区别</li> <li>语法格式如下：</li></ul> <div class="language-python line-numbers-mode"><pre class="language-python"><code><span class="token keyword">if</span> 条件 <span class="token number">1</span><span class="token punctuation">:</span>
    条件 <span class="token number">1</span> 满足执行的代码
    ……
    
    <span class="token keyword">if</span> 条件 <span class="token number">1</span> 基础上的条件 <span class="token number">2</span><span class="token punctuation">:</span>
        条件 <span class="token number">2</span> 满足时，执行的代码
        ……    
        
    <span class="token comment"># 条件 2 不满足的处理</span>
    <span class="token keyword">else</span><span class="token punctuation">:</span>
        条件 <span class="token number">2</span> 不满足时，执行的代码
        
<span class="token comment"># 条件 1 不满足的处理</span>
<span class="token keyword">else</span><span class="token punctuation">:</span>
    条件<span class="token number">1</span> 不满足时，执行的代码
    ……
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br></div></div><h4 id="if-的嵌套-演练-火车站安检"><a href="#if-的嵌套-演练-火车站安检" class="header-anchor">#</a> if 的嵌套 演练 —— 火车站安检</h4> <p><strong>需求</strong></p> <ol><li>定义布尔型变量 <code>has_ticket</code> 表示是否有车票</li> <li>定义整型变量 <code>knife_length</code> 表示刀的长度，单位：厘米</li> <li>首先检查是否有车票，如果有，才允许进行 <strong>安检</strong></li> <li>安检时，需要检查刀的长度，判断是否超过 20 厘米
<ul><li>如果超过 20 厘米，提示刀的长度，不允许上车</li> <li>如果不超过 20 厘米，安检通过</li></ul></li> <li>如果没有车票，不允许进门</li></ol> <div class="language-python line-numbers-mode"><pre class="language-python"><code><span class="token comment"># 定义布尔型变量 has_ticket 表示是否有车票</span>
has_ticket <span class="token operator">=</span> <span class="token boolean">True</span>

<span class="token comment"># 定义整数型变量 knife_length 表示刀的长度，单位：厘米</span>
knife_length <span class="token operator">=</span> <span class="token number">20</span>

<span class="token comment"># 首先检查是否有车票，如果有，才允许进行 安检</span>
<span class="token keyword">if</span> has_ticket<span class="token punctuation">:</span>
    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;有车票，可以开始安检...&quot;</span><span class="token punctuation">)</span>

    <span class="token comment"># 安检时，需要检查刀的长度，判断是否超过 20 厘米</span>
    <span class="token comment"># 如果超过 20 厘米，提示刀的长度，不允许上车</span>
    <span class="token keyword">if</span> knife_length <span class="token operator">&gt;=</span> <span class="token number">20</span><span class="token punctuation">:</span>
        <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;不允许携带 %d 厘米长的刀上车&quot;</span> <span class="token operator">%</span> knife_length<span class="token punctuation">)</span>
    <span class="token comment"># 如果不超过 20 厘米，安检通过</span>
    <span class="token keyword">else</span><span class="token punctuation">:</span>
        <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;安检通过，祝您旅途愉快……&quot;</span><span class="token punctuation">)</span>

<span class="token comment"># 如果没有车票，不允许进门</span>
<span class="token keyword">else</span><span class="token punctuation">:</span>
    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;大哥，您要先买票啊&quot;</span><span class="token punctuation">)</span>

</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br></div></div><h2 id="_05-综合应用-石头剪刀布"><a href="#_05-综合应用-石头剪刀布" class="header-anchor">#</a> 05. 综合应用 —— 石头剪刀布</h2> <p><strong>目标</strong></p> <ol><li>强化 <strong>多个条件</strong> 的 <strong>逻辑运算</strong></li> <li>体会 <code>import</code> 导入模块（“工具包”）的使用</li></ol> <p><strong>需求</strong></p> <ol><li>从控制台输入要出的拳 —— 石头（1）／剪刀（2）／布（3）</li> <li>电脑 <strong>随机</strong> 出拳 —— 先假定电脑只会出石头，完成整体代码功能</li> <li>比较胜负</li></ol> <table><thead><tr><th style="text-align:center;">序号</th> <th style="text-align:center;">规则</th></tr></thead> <tbody><tr><td style="text-align:center;">1</td> <td style="text-align:center;">石头 胜 剪刀</td></tr> <tr><td style="text-align:center;">2</td> <td style="text-align:center;">剪刀 胜 布</td></tr> <tr><td style="text-align:center;">3</td> <td style="text-align:center;">布 胜 石头</td></tr></tbody></table> <h3 id="_5-1-基础代码实现"><a href="#_5-1-基础代码实现" class="header-anchor">#</a> 5.1 基础代码实现</h3> <ul><li>先 <strong>假定电脑就只会出石头</strong>，完成整体代码功能</li></ul> <div class="language-python line-numbers-mode"><pre class="language-python"><code><span class="token comment"># 从控制台输入要出的拳 —— 石头（1）／剪刀（2）／布（3）</span>
player <span class="token operator">=</span> <span class="token builtin">int</span><span class="token punctuation">(</span><span class="token builtin">input</span><span class="token punctuation">(</span><span class="token string">&quot;请出拳 石头（1）／剪刀（2）／布（3）：&quot;</span><span class="token punctuation">)</span><span class="token punctuation">)</span>

<span class="token comment"># 电脑 随机 出拳 - 假定电脑永远出石头</span>
computer <span class="token operator">=</span> <span class="token number">1</span>

<span class="token comment"># 比较胜负</span>
<span class="token comment"># 如果条件判断的内容太长，可以在最外侧的条件增加一对大括号</span>
<span class="token comment"># 再在每一个条件之间，使用回车，PyCharm 可以自动增加 8 个空格</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token punctuation">(</span>player <span class="token operator">==</span> <span class="token number">1</span> <span class="token keyword">and</span> computer <span class="token operator">==</span> <span class="token number">2</span><span class="token punctuation">)</span> <span class="token keyword">or</span>
        <span class="token punctuation">(</span>player <span class="token operator">==</span> <span class="token number">2</span> <span class="token keyword">and</span> computer <span class="token operator">==</span> <span class="token number">3</span><span class="token punctuation">)</span> <span class="token keyword">or</span>
        <span class="token punctuation">(</span>player <span class="token operator">==</span> <span class="token number">3</span> <span class="token keyword">and</span> computer <span class="token operator">==</span> <span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">:</span>

    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;噢耶！！！电脑弱爆了！！！&quot;</span><span class="token punctuation">)</span>
<span class="token keyword">elif</span> player <span class="token operator">==</span> computer<span class="token punctuation">:</span>
    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;心有灵犀，再来一盘！&quot;</span><span class="token punctuation">)</span>
<span class="token keyword">else</span><span class="token punctuation">:</span>
    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;不行，我要和你决战到天亮！&quot;</span><span class="token punctuation">)</span>

</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br></div></div><h3 id="_5-2-随机数的处理"><a href="#_5-2-随机数的处理" class="header-anchor">#</a> 5.2 随机数的处理</h3> <ul><li>在 <code>Python</code> 中，要使用随机数，首先需要导入 <strong>随机数</strong> 的 <strong>模块</strong> —— “工具包”</li></ul> <div class="language-python line-numbers-mode"><pre class="language-python"><code><span class="token keyword">import</span> random
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><ul><li><p>导入模块后，可以直接在 <strong>模块名称</strong> 后面敲一个 <code>.</code> 然后按 <code>Tab</code> 键，会提示该模块中包含的所有函数</p></li> <li><p><code>random.randint(a, b)</code> ，返回 <code>[a, b]</code> 之间的整数，包含 <code>a</code> 和 <code>b</code></p></li> <li><p>例如：</p></li></ul> <div class="language-python line-numbers-mode"><pre class="language-python"><code>random<span class="token punctuation">.</span>randint<span class="token punctuation">(</span><span class="token number">12</span><span class="token punctuation">,</span> <span class="token number">20</span><span class="token punctuation">)</span>  <span class="token comment"># 生成的随机数n: 12 &lt;= n &lt;= 20   </span>
random<span class="token punctuation">.</span>randint<span class="token punctuation">(</span><span class="token number">20</span><span class="token punctuation">,</span> <span class="token number">20</span><span class="token punctuation">)</span>  <span class="token comment"># 结果永远是 20   </span>
random<span class="token punctuation">.</span>randint<span class="token punctuation">(</span><span class="token number">20</span><span class="token punctuation">,</span> <span class="token number">10</span><span class="token punctuation">)</span>  <span class="token comment"># 该语句是错误的，下限必须小于上限</span>
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